Harmonic drive register adjustment device for a printing press

ABSTRACT

A printing press includes a first printing unit having a first blanket cylinder for printing one side of sheet material and a first plate cylinder associated with the first blanket cylinder for transferring an image to the first blanket cylinder. The printing press also includes a second blanket cylinder for printing the other side of the sheet material and a second plate cylinder associated with it for transferring an image thereto. The first and second blanket cylinders are positioned such that the images received by the respective plate cylinders are applied to the sheet material simultaneously. A register adjusting device circumferentially adjusts the relative positions of plate cylinders so that registry is maintained between the images applied to the sheet material. The adjusting means includes a harmonic drive unit drivingly connected to one of the plate cylinders so that the rotational position of that plate cylinder with respect to the other plate cylinder may be varied thereby.

United States Patent 1 Treff [111 3,724,368 1 Apr. 3, 1973 [54] HARMONIC DRIVE REGISTER ADJUSTMENT DEVICE FOR A PRINTING PRESS [75] Inventor: Ernest H. Treit, Groton, Conn.

[73] Assignee: Harris-Intertype C0rporation,Cleveland, Ohio [22] Filed: June 17, 1970 [21] Appl. No.: 47,048

[52] 0.8. CI ..l01/248, 101/247 [51] Int. Cl. ..B41f 13/12 [58] Field of Search ..101/248, 247, 220

[56] References Cited UNITED STATES PATENTS 1,320,358 10/1919 Bacon ..l01/247 UX 2,301,379 11/1942 Davis ..101/248 2,949,851 8/1960 Ghormley, Jr. et al.. 101/248 2,906,143 9/1959 Musser ..74/640 3,329,086 7/1967 Pullen ..101/220 X 3,565,006 2/1971 Stewart 101/248 3,525,305 8/1970 Daniels ..l01/248 X 3,511,179 5/1970 Breunig.... ..l01/248 X 3,218,969 11/1965 Nagel ..101/248 X 3,073,997 1/1963 Tagliasacchi ..101/248 X 1,590,742 6/1926 Goulding ..l01/220 X 3,527,165 9/1970 Harless ..101/220 X 2,248,926 7/1941 Meisel ..101/220 OTHER PUBLICATIONS Rigid Indexing Coupling Uses Harmonic Drive Principle, by Victor W. Wigotsky; from April 28, 1965 Design News; Cahners Pub.

I Use Harmonic ori'fifiiiglrnafio" Differentials,

from Feb. 1967, Power Transmission Design, Industrial Publishing Co. Delrin Selected for Harmonic Drive," Engineering Design 67/1 E. I. du Pont de Nemours & Co.

Power Plant Employs Harmonic Drive Reducer Dec. 1965, Pacific Factory.

Compact I-Iigh Reduction Single Stage, July 1966 Power Transmission Design.

Primary Examiner-Robert E. Pulfrey Assistant Examiner-R. E. Suter Attorney-Yount and Tarolli [57] ABSTRACT A printing press includes a first printing unit having a first blanket cylinder for printing one side of sheet material and a first plate cylinder associated with the first blanket cylinder for transferring an image to the first blanket cylinder. The printing press also includes a second blanket cylinder for printing the other side of the sheet material and a second plate cylinder associated with it for transferring an image thereto. The first and second blanket cylinders are positioned such that the images received by the respective plate cylinders are applied to the sheet material simultaneously. A register adjusting device circumferentially adjusts the relative positions of plate cylinders so thatregistry is maintained between the images applied to the sheet material. The adjusting means includes a harmonic drive unit drivingly connected to one of the plate cylinders so that the rotational position of that plate cylinder with respect to the other plate cylinder may be varied thereby.

2 Claims, 6 Drawing Figures HARMONIC DRIVE REGISTER ADJUSTMENT DEVICE FOR A PRINTING PRESS The present invention relates to a printing press, and, more particularly, relates to a register adjusting device for circumferentially adjusting the position of a plate cylinder relative to a blanket cylinder in an offset printing press.

Printing presses have included mechanisms for circumferentially adjusting one cylinder of the press relative to another cylinder. In offset presses such adjustments have been used in conjunction with a plate cylinder to circumferentiaily adjust the position of the plate cylinder relative to a blanket cylinder. In perfecting blanket-to-blanket presses, such an adjustment provides for registry of the images printed on the opposite sides of the material relative to each other. In multicolor presses, such adjustments provide for the registry of images printed in one unit with the images printed in another unit.

The prior art mechanisms for circumferentially adjusting a plate cylinder relative to a blanket cylinder have been quite intricate. One common mechanism for performing this circumferential adjustment includes helical gears, one of which moves axially relative to the other to thereby effect rotation of one of the gears which was drivingly connected with the plate cylinder to thereby adjustably rotate the plate cylinder. In perfecting presses where the plate cylinder was intergeared with another cylinder, compensation or provision had to be made for preventing corresponding rotation of the cylinder which was drivingly connected with the plate cylinder. As a result, such known mechanisms are complicated in construction and expensive to manufacture.

The immediate invention solves these problems of the prior art devices by providing a register adjusting device for the plate cylinder of an offset printing press which is simplified in design. The register adjusting device of the present invention includes a harmonic drive unit drivingly connected to the plate cylinder of the printing press. When the image is out of registry, the harmonic drive is actuated so as to circumferentially rotate the plate cylinder relative to its cooperating blanket cylinder. The design is extremely simple and does not require other compensation devices as are required in the afore-mentioned prior art.

Accordingly, it is an object of the present invention to provide a new and improved circumferential register adjustment mechanism for the plate cylinder of an offset printing press and which mechanism is simple in construction, inexpensive to manufacture, highly effective in operation, allows register adjustments to be made while the printing press is in operation, and does not require the aforementioned compensation provi-' sion.

A further object of the present invention is to provide a new and improved register adjusting device for an offset printing press wherein the register adjusting mechanism includes a harmonic drive unit drivingly connected to a plate cylinder which cooperates with a blanket cylinder and which is adapted to rotate the plate cylinder relative to the blanket cylinder to provide circumferential adjustment therebetween.

A still further object of the present invention is the provision of a new and improved register adjusting device for perfecting printing press which includes a harmonic drive unit having an input member driven at a speed proportional to the speed of a blanket cylinder associated with a plate cylinder, an output member adapted to be driven by the input member and'drivingly connected to the plate cylinder, and a wave generator for creating driving engagement between the input and output members and which is rotated tovadjust the register of the printed image with respect to the sheet material.

Further objects, advantages, and features of the present invention will be apparent to those skilled in the art to which it relates from the following detailed description of a preferred embodiment thereof, made with reference to the accompanying drawings forming a part of this specification and in which:

FIG. 1 is a schematic view of a portion of a printing press embodying the immediate invention;

FIG. 2 is a sectional view of the printing unit shown in FIG. 1;

FIG. 3 is another schematic view of the printing unit shown in FIG. 1;

FIG. 4 is an enlarged view of a portion of the printing unit shown in FIG. 2;

FIG. 5 is a representative view of the portion of the printing unit of FIG. 4, taken along the lines 5-5 thereof; and

FIG. 6 is a schematic view of a pair of printing units of the printing press of the present invention. 7

The present invention provides a new and improved register adjusting mechanism for the plate cylinder of an offset printing press. The register adjusting mechanism of the present invention is of a simplified construction and provides for register adjustment while the printing press is in motion. The register adjusting mechanism of the present invention also allows for register adjustment to be made between printing units and between the blanket-to-blanket cylinders of the printing units. The present invention may be applied to printing presses of a wide variety of constructions and designs and for purposes of illustration is described in the drawings as applied to an offset perfecting printing press 10, schematically shown in FIG. 1.

The printing press 10 has a printing unit 11 which includes a pair of blanket cylinders 12, 14 defining a printing nip 15 therebetween. The blanket cylinders 12, 14 are rotatably mounted to the press frame 101 by bearings 53, 56 (See FIG. 2), respectively, and have plate cylinders 16, 18 associated therewith, respectively, which transfer an image to the respective blanket cylinders 12, 14. The blanket cylinders 12, 14 are positioned so that material 20 may pass the'rebetween through the printing nip l5 and will be printed on both sides thereof simultaneously by the blanket cylinders 12, 14. The printing press 10 may also include other printing units similar to the printing unit 11.

One of the blanket cylinders 14 is driven by a suitable drive means 22 which is drivingly connected to the shaft 24 extending from the blanket cylinder 14. The drive for the shaft 24 will not be described in detail, since it does not form a part of the present invention. Gears 26, 28 are suitably secured to the shaft 24 of the blanket cylinder 14 and are rotated by the drive means 22. Gears 30, 32 are secured to a shaft 34 extending from the blanket cylinder 12. The gear 26 is in a meshing relationship with the gear 30. The gears 28, 32 rotate with gears 26, 30 and drive the plate cylinders 16, 18, respectively.

Means for circumferentially adjusting the relative positions of the plate cylinders 16, 18, schematically indicated at 36, 38, in FIG. 1, respectively, includes harmonic drive units 40, 42. The harmonic drive units 40, 42 include input members 44, 46, respectively. The input members 44, 46 have gear portions 48, 50 associated therewith respectively. The gear portions 48, 50 mesh with the gears 32, 28, respectively. Since the gears 28, 32 are secured to the shafts 24, 34, respectively, and, consequently, rotate therewith, the gears 28, 32 rotate the input members 46, 44 of the harmonic drive units 42, 40, respectively, as a result of the meshing of the gear teeth 50, 48 with the gears 28, 32, respectively. Thus, it should be understood that the input members 44, 46 of the harmonic drive units 40, 42 are rotated at a speed proportional to the speed of the blanket cylinders 12, 14.

The gears associated with the blanket cylinders 12, 14 and plate cylinders 16, 18 have a predetermined number of teeth thereon. The number of gear teeth on the gears 26, 30 of the blanket cylinders 14, 12, respectively, are equal so that the blanket cylinders 12, 14 are rotated at the same peripheral speed.

The plate cylinders 16, 18, as shown in the disclosed embodiment, must be driven at the same peripheral speed as their respective blanket cylinders 12, 14 for proper transfer of the image thereto. Since the plate cylinders 16, 18 have a diameter equal to one-half the diameter of the blanket cylinders 12, 14, respectively, the gear ratio existing between the blanket cylinders l2, l4 and the plate cylinders 16, 18, respectively, must be equal to 2 to l in order for the peripheral speed of the plate cylinders to be equal to the peripheral speed of their respective blanket cylinders. The gears 28, 32 have a greater number of teeth than the gear portions 48, 50 of the input members 44, 46. The harmonic units 40, 42 have a variable drive ratio so that the input members 44, 46 have a speed greater than the speed of their output members to which the plate cylinders 16, 18 are attached. Drive means 52, 54 are drivingly connected to the harmonic drive units 40, 42, respectively, so that upon actuation thereof the register of the images applied to the blanket cylinders 12, 14 by the plate cylinders 16, 18, respectively, may be adjusted.

It should be understood that the printing press may also include other printing units, such as the printing unit 13, as shown in FIG. 6. The printing unit 13 includes a pair of blanket cylinders 17, 19 which are constructed in a manner similar to that described in connection with the blanket cylinders 12, 14, respectively, of the printing unit 11. The blanket cylinders 17, 19 have complementary harmonic drive units connected thereto to adjust the register of their printing images with respect to each other and the images of the printing unit 11.

FIG. 2 shows the gears 26, 30 mounted to the shafts 24, 34 of the blanket cylinders l4, 12, respectively. In a like manner, the gears 32, 28 are secured to the shafts 34, 24 of the blanket cylinders. The gears 28, 32 are secured to the shafts 24, 34 by means of keys 55. The keys 55 prohibit rotation of the gears 28, 32 with respect to their respective shafts 24, 34. The gears 26,

30 are secured to their respective gears 28, 32 by means of the threaded fasteners 58, so that each of the pairs of gears30, 32 and 26, 28 rotate about their respective axes of their respective shafts 34, 24. It,

should be understood that the rotational axes of the shafts 24, 34 are positioned so that the gears 26, 30 are in meshing engagement with each other.

The harmonic drive units 40, 42 are similar in construction and drive their corresponding plate cylinders 16, 18 in substantially the same manner. In addition, their input members 44, 46 are driven by the gears 32, 28 in a similar manner. Due to this similarity of the harmonic drive units 40, 42, the description of the harmonic drive unit 42 which follows is equally applicable to the harmonic drive unit 40, schematically shown in FIG. 1. The harmonic drive unit 42 is driven by the gear 28 in a manner so that the plate cylinder 18 is rotated thereby. It should be understood that the harmonic drive unit 40 is driven by the gear 32 in a similar manner so that the plate cylinder 16 is rotated in a corresponding manner.

The gear portion 50 of the input member 46 of the harmonic drive unit 42 is adapted to mesh with and be driven by the gear 28. The input member 46 is rotatably supported by the bearings about the shaft 63 of the plate cylinder 18. The number of gear teeth on the input member 46 is predetermined with respect to the number of gear teeth on the gear 28 so that a predetermined ratio between the speeds of the input member 46 and gear 28 is achieved.

In the disclosed embodiment, the plate cylinder 18 is shown to have a diameter equal to one-half the diameter of the blanket cylinder 14. In order for the peripheral speed of the plate cylinder 18 to be equal to the peripheral speed of the blanket cylinder 14, it must be rotated at twice the rotational speed. If the input member 46 were directly connected to the plate cylinder 18, the peripheral speeds of the plate cylinder 18 and the blanket cylinder 14 would be equal, if the pitch diameter of the gear 28 were twice the pitch diameter of the gear portion 50 of the input member 46 or the gear 28 had twice the number of teeth of the gear portion 50. In the disclosed embodiment, the number of gear teeth on the gear 28 is less than that required to rotate the plate cylinder 18 at a peripheral speed equal to the blanket cylinder 14, and, consequently, if the input member 46 were directly connected to the plate cylinder 18, the plate cylinder 18 would rotate at the slightly lower speed than the blanket cylinder 14.

The drive connection between the input member 46 and output member 64 compensates for the lower rotational speed of the input member 46. The input member 46 has a predetermined number of internal gear teeth 62 which mesh with the external gear teeth 66 of the output member 64. The number of external gear teeth 66 on the output member 64 are less than the number of internal gear teeth on the input member 46. Thus, the output member 64 rotates at a greater rotational speed than the input member 46, as shown hereinafter.

The number of gear teeth on the gear 28 and the gear portion 50 of the input member are designed so that when the blanket cylinder 14 is rotated at a certain peripheral speed, the input member 46 rotates at a peripheral speed slightly lower than that of the blanket cylinder 14, as hereinabove described. The gear 28 drives the input member 46 through the gear portion 50, through which the torque is transmitted to the output member 64 through the meshing gear portions, and the plate cylinder 18 is thereby rotated. The number of gear teeth on the gear 28, the gear portion 50 of the input member 46, the internal gear teeth 62 of the input member and the number of external teeth 66 on the output member are such that the plate cylinder 18 is rotated at a peripheral speed equal to the peripheral speed of the blanket cylinder 14.

The output member 64 is manufactured from a flexible material, such as steel or plastic, so that it may be deformed by a wave generator 68 to position a portion of the external gear teeth 66 on the output member 64 in meshing engagement with a portion of the internal gear teeth 62 on the input member 46. When the wave generator 68 is stationary, and the input member 46 is rotated, the output member 64 will rotate at a speed greater than the rotational speed of the input member 46, since the number of internal teeth 62 on the input member is greater than the number of external teeth 66 on the output member 64.

The relationship between the number of teeth on the drive train connecting the blanket cylinder 14 to the plate cylinder 18 is predetermined so that the blanket cylinder 14 drives the plate cylinder 18 at twice the rotational speed when the wave generator 68 is stationary so that the peripheral speeds of the blanket cylinder 14 and the plate cylinder 18 will be equal. For example, if there are 119 teeth on the gear 28 and 60 teeth on the gear portion 50 of the input member 46, the input member 46 will rotate at a speed slightly less than twice the rotational speed of the gear 28. The wave generator 68 deforms the output member 64 such that a portion of its gears contacts the internal gear teeth 62 of the input members 46. If there are 240 internal gear teeth, indicated at 62, on the input member 46, and 238 external gear teeth on the output member 64, the output member 64 will rotate at a slightly higher speed than the input member 46. Using the number of teeth hereinabove described, it may be calculated that the output member 64 rotates at exactly twice the speed of the gear 28 when the wave generator 68 is stationary. Since the output member 64 is drivingly connected to the plate cylinder 18, the plate cylinder 18 rotates at exactly twice the speed of the blanket cylinder 14, and, consequently, the peripheral speeds of the blanket cylinder 14 and plate cylinder 18 are equal.

The output member 64 of the harmonic drive 42 is secured to the shaft 63 of the plate cylinder 18 and is positioned between the two plates 70, 72. Openings 74 are provided in the plates 70, 72 and output member 64 so that the threaded fastener 76 may pass therethrough and be threadedly engaged by the end of the shaft 63 of the plate cylinder 18. Thus, torque is transmitted from the output member 64 to the shaft 63 and the plate cylinder 18. The shaft 63 rotatably supports the bearings 60 so that input member 36 is rotatably supported about the rotational axis of the shaft 63.

In order to adjust the register of the image transferred from the plate cylinder 18 to the blanket cylinder 14, it is necessary to rotate the plate cylinder 18 with respect to the blanket cylinder 14 in a precise and accurate manner. In order to accomplish this objective, a drive means 54, such as the stepping motor 78, is drivingly connected to the wave generator 68 by the shaft 80.

The shaft is keyed to the wave generator 68 such that the wave generator 68 rotates with the shaft 80. The shaft 80 is rotatably supported in bearings 82 which are retained by the member 84 secured to the press frame. A coupling device 86 of conventional design is provided to connect the stepping motor 78 to the shaft 80. A control unit, schematically shown at 88, is connected to the stepping motor 78 such that the stepping motor 78 may be rotated in either direction which may be determined by the printing press operator. By actuating the control device 88, the stepping motor 78 is rotated a predetermined amount in a predetermined direction and, consequently, the wave generator 68 is rotated. When the wave generator 68 is rotated, the position of the portion of the external gears 66 on the output member 64 engaging the internal gears 62 on the input member 46 moves with respect to the input member 46 and, thus, the phase relationship between the plate cylinder 18 and blanket cylinder 14 is changed. Consequently, the position of the image transferred to the blanket cylinder 14 by the plate cylinder 18 is varied with respect to the remainder of the images printed by the press. A detailed description of the harmonic drive unit can be obtained by reference to U.S. Pat. No. 2,906,143, which further explains the operation of the wave generator and the phase change brought about thereby.

It should be understood that the stepping motor 78 may be rotated in either direction so that the registry of the images transferred to the blanket cylinder 14 may be adjusted in either direction. The stepping motor 78 is designed such that it prohibits the shaft 80 from rotating when the stepping motor 78 is not rotated. Thus, the gear ratio of two-to-one between the blanket cylinder 14 and plate cylinder 18 is thereby maintained when the stepping motor 78 is not actuated.

The printing press 10 also includes a throwoff mechanism, as seen in FIG. 3 and generally indicated 100, which moves the blanket cylinders 12, 14 away from each other and their respective plate cylinders 16, 18. It should be understood that the throwoff mechanism may be of any conventional design and the design shown in FIG. 3 is merely representative of one design. The'throwoff mechanism 100 includes an actuator, such as an air cylinder 102 for creating such movement. One end of the cylinder 102 is pivotally mounted to a mounting bracket 104 which is in turn secured to the frame 101 of the printing press. The rod 106 of the cylinder 102 is pivotally secured to the arm 111 of a crank member 108 about the axis 110 of the arm 111. The crank member 108 is pivotally mounted about a pin 112 secured .to the frame 101 of the printing press 10 and rotates thereabout. The other arm 114 of the crank member 108 is pivotally mounted to a link 116 about the axis 118.

The link 1 16 is also pivotally connected, as shown in FIG. 3, to an eccentric 120 which supports the bearings 56 associated with the blanket cylinder 14. When the crank member 108 is rotated by the piston 102 from a first position, generally indicated at 124, to a second position 126, the eccentric 120 moves the blanket cylinder 14 from a printing position 128 to a disengaged, nonprinting position 130. ln'the printing posi tion 128, the blanket cylinder 14 is in a printing relationship with respect to the plate cylinder 18 of the blanket cylinder 12. When the blanket cylinder 14 is in the disengaged position 130, the blanket cylinder 14 is out of engagement with the plate cylinder 18 and blanket cylinder 12 so that the sheet material may pass through the printing nip defined by the blanket cylinders 12, 14 without marking or printing of the sheet material. I

The throwoff mechanism 100 also includes a connecting link 132 secured to the eccentric member 120 of the blanket cylinder 14 which is connected to an eccentric member 134 which supports the bearings 53 associated with the blanket cylinder 12. When the blanket cylinder 14 is in a disengaged position 130, the blanket cylinder 12 is also moved in a disengaged position 136, since the link 132 moves the eccentric 134 when the eccentric 120 is moved. Correspondingly, when the blanket cylinder 14 is in a printing position 128, the blanket cylinder 12 is in a printing position 138. When the blanket cylinders l2, 14 are in a nonprinting position 130, 136, the gears 26 and 30 remain in meshing engagement with each other. This enables the cylinders to be rotated thereby for make-up and other purposes when the blanket cylinders are in nonprinting position. The intermeshing gears 28, 32 still have their teeth in mesh when the blanket cylinders are in non-printing position. However, the overlap of the gear teeth is slight, since their pitch diameters are less than the pitch diameters of gears 26, 30, hence they are only in partial engagement even before the cylinders are thrown off impression. Due to this slight overlap, these gears, when the blanket cylinders are thrown off, may not reliably carry the drive forces for driving the cylinders. This makes gears 26, 30 important for driving the cylinders when the blanket cylinders are in nonprinting position.

What is claimed is: 1. A printing press comprising, first and second cylinders defining a printing nip and having a first position in which said cylinders are cooperable to print on at least one side of material advanced through the nip, said first and second cylinders comprising a blanket cylinder and another cylinder,

a plate cylinder cooperable with the blanket cylinder for transferring an image to the blanket cylinder, throw-off means for bodily relatively moving said first-cylinder and said second cylinder away from said first position to a second position and from said second position toward each other to said first position, means for drivingly interconnecting said first and second cylinders when in their first and second positions, said means comprising, first and second gear means, means for drivingly connecting said first gear means to said first cylinder, means for drivingly connecting said second gear means to said second cylinder, said first and second gear means having gear teeth which are engaged to provide a drive therebetween when the cylinders are in their first and second positions,

third gear means having gear teeth in a meshing driving relation with gear teeth of said first gear means when said first and second cylinders are in both said first and second positions,

means drivingly connecting said third gear means with said plate cylinder,

the number of gear teeth on said first gear means meshing with the gear teeth of said third gear means being less than that required to rotate said plate cylinder at the surface speed of said blanket cylinder,

said means drivingly connecting said third gear means with said plate cylinder comprising a differential harmonic drive unit for providing rotation of said plate cylinder relative to said third gear means, said differential harmonic drive unit comprising,

an input member drivingly connected with said third gear means, said input member having a predetermined number of internal gear teeth thereon,

a deformable output member drivingly connected to said plate cylinder and having a number of external gear teeth thereon less than the predetermined number of internal gear teeth on said input member and positioned such that said external gear teeth of said output member are fully meshing along a portion of the periphery thereof with said internal gear teeth,

the number of said internal gear teeth and said ex ternal gear teeth being such as to compensate for the reduced number of gear teeth on said first gear means so that said plate cylinder is rotated at the surface speed of said blanket cylinder,

a wave generator member movable relative to said output member to deform said output member such that the portion of said external gear teeth thereon meshing with a portion of said internal gear teeth on said input member varies to thereby vary the circumferential position of said plate cylinder relative to said third gear means,

a motor means drivingly connected to said wave generator member to effect rotation of said wave generator member upon actuation thereof,

said first gear means comprising a first pair of gears and said second gear means comprises a second pair of gears,

said first pair of gears comprising first and second gears,

said second pair of gears comprising fourth and fifth gears,

said first and fourth gears and said second and fifth gears respectively having an equal number of teeth which have a meshing relationship when said first and second cylinders are in their printing position as well as when said cylinders are in their second position,

said first gear having gear teeth in a meshing relationship with said third gear means, and

said first and fourth gears having a smaller pitch diameter than said second and fifth gears, and the number of gear teeth on said first gear meshing with said third gear means compensating for the difference in the number of gear teeth between said internal and external gear teeth so that'said 9 l blanket and plate cylinders are rotated at the same sixth gear means having a meshing relationship with surface speed. said fourth gear,

2. A printing press as defined in claim 1 wherein said means drivingly connecting said other plate cylinder second cylinder comprises a blanket cylinder for printand d I h g a m ans including a differential ing on the other side of the material advanced through 5 harmonic dl'we mm for Provldmg rotatlon 0f Sald the nip, and further including, other plate cylinder relative to said sixth gear another plate cylinder cooperable with said second means' cylinder and, I 

1. A printing press comprising, first and second cylinders defining a printing nip and having a first position in which said cylinders are cooperable to print on at least one side of material advanced through the nip, said first and second cylinders comprising a blanket cylinder and another cylinder, a plate cylinder cooperable with the blanket cylinder for transferring an image to the blanket cylinder, throw-off means for bodily relatively moving said first cylinder and said second cylinder away from said first position to a second position and from said second position toward each other to said first position, means for drivingly interconnecting said first and second cylinders when in their first and second positions, said means comprising, first and second gear means, means for drivingly connecting said first gear means to said first cylinder, means for drivingly connecting said second gear means to said second cylinder, said first and second gear means having gear teeth which are engaged to provide a drive therebetween when the cylinders are in their first and second positions, third gear means having gear teeth in a meshing driving relation with gear teeth of said first gear means when said first and second cylinders are in both said first and second positions, means drivingly connecting said third gear means with said plate cylinder, the number of gear teeth on said first gear means meshing with the gear teeth of said third gear means being less than that required to rotate said plate cylinder at the surface speed of said blanket cylinder, said means drivingly connecting said third gear means with said plate cylinder comprising a differential harmonic drive unit for providing rotation of said plate cylinder relative to said third gear means, said differential harmonic drive unit comprising, an input member drivingly connected with said third gear means, said input member having a predetermined number of internal gear teeth thereon, a deformable output member drivingly connected to said plate cylinder and having a number of external gear teeth thereon less than the predetermined number of internal gear teeth on said input member and positioned such that said external gear teeth of said output member are fully meshing along a portion of the periphery thereof with said internal gear teeth, the number of said internal gear teeth and said external gear teeth being such as to compensate for the reduced number of gear teeth on said first gear means so that said plate cylinder is rotated at the surface speed of said blanket cylinder, a wave generator member movable relative to said output member to deform said output member such that the portion of said external gear teeth thereon meshing with a portion of said internal gear teeth on said input member varies to thereby vary the circumferential position of said plate cylinder relative to said third gear means, a motor means drivingly connected to said wave generator member to effect rotation of said wave generator member upon actuation thereof, said first gear means comprising a first pair of gears and said second gear means comprises a second pair of gears, said first pair of gears comprising first and second gears, said second pair of gears comprising fourth and fifth gears, said first and fourth gears and said second and fifth gears respectively having an equal number of teeth which have a meshing relationship when said first and second cylinders are in their printing position as well as when said cylinders are in their second position, said first gear having gear teeth in a meshing relationship with said third gear means, and said first and fourth gears having a smaller pitch diameter than said second and fifth gears, and the number of gear teeth on said first gear meshing with said third gear means compensating for the difference in the number of gear teeth between said internal and external gear teeth so that said blanket and plate cylinders are rotated at the same surface speed.
 2. A printing press as defined in claim 1 wherein said second cylinder comprises a blanket cylinder for printing on the other side of the material advanced through the nip, and further including, another plate cylinder cooperable with said second cylinder and, sixth gear means having a meshing relationship with said fourth gear, means drivingly connecting said other plate cylinder and said sixth gear means including a differential harmonic drive unit for providing rotation of said other plate cylinder relative to said sixth gear means. 